What’s the reason for ashes on Ash Wednesday?

I got this article from this site: http://www.kencollins.com/question-02.htm

As you know, Jesus retreated into the wilderness and fasted for forty days to prepare for his ministry. It was for Him a time of contemplation, reflection, and preparation. By observing Lent, most Christians join Jesus on His retreat.
Lent consists of the forty days before Easter. In the western Church, we skip over the Sundays when we count the days of Lent, because Sunday is always the joyful celebration of the Resurrection. Therefore, the first day of Lent in the western Church is always a Wednesday.
Biblical societies relied very heavily on wood fires for heating and cooking, which meant that keeping ashes under control was a major housekeeping task. Then as now, if a person was preoccupied with something serious, they didn’t always tend to the housekeeping—it’s the least of their concerns. Imagine that there is a death in the family. A friend stopping by to pay their respects might gently say, “Did you know you have ashes on your face?”
So ashes became a sign of remorse, repentance, and mourning. Today someone might wear a black armband to signify that they are in mourning; back then people put ashes on their foreheads.
You can find biblical examples of this in 2 Samuel 13:19, Esther 4:1-3, Job 42:6, and Jeremiah 6:26. During Lent, ancient Christians mourned their sins and repented of them, so it was appropriate for them to show their sincerity by having ashes on their foreheads. The custom has persisted in the church as secular society has changed around us.
It is most appropriate on Ash Wednesday, when we begin a period of sober reflection, self-examination, and spiritual redirection.
Traditionally, the ashes for the Ash Wednesday service come from burning the palm fronds from the previous year’s Palm Sunday celebration. If you burn the palm fronds yourself, don’t add any other ingredient—just burn the ashes plain. Add a little oil to the ashes so that they will stick to people’s foreheads. Of course, it is easier to purchase them from a religious supply house. Don’t overestimate how much you need! It is amazing how far a small amount of ashes will go!
Some people only celebrate the happy times in Jesus’ life: Palm Sunday, Easter Sunday, and Christmas. But I think as true friends, we should also watch and pray with Him on Maundy Thursday, stand by Him at the cross on Good Friday, and retreat with Him into the wilderness during Lent. You can read more about Jesus’ fair-weather friends.
About fasting: Today the word ‘fasting’ means a total abstention from all food. In the historic Church, it means a disciplined diet so that your animal appetites become a sort of spiritual snooze alarm. You can read information about fasting.
You get more information about Lent. You can also read Honest to God for an explanation of what we accomplish by observing Lent.